Recently, Worldwide Interoperability for Microwave Access (WiMAX) has attracted attention as a wireless communication technology capable of high-speed and long-distance transmission. WiMAX systems assume application to a network using an IP protocol and implement a mobile service by combining a Layer 3 mobility technology (mobile IP) and a Layer 2 mobility technology based on the technology of IEEE 802.16e.
Currently, protocol specifications are developed by the WiMAX Forum, which is an industry organization. To provide a mobile service utilizing a WiMAX system to mobile terminals not equipped with a mobile IP function, a “proxy mobile IP scheme” is under study to provide client function of the mobile IP on the network side. To implement a method of adding IP addresses to mobile terminals as a mode using Dynamic Host Configuration Protocol (DHCP) widely utilized in Internet access services, a mode of providing a DHCP proxy function on the network side is under discussion.
FIG. 9 depicts a configuration of a WiMAX system in the proxy mobile IP scheme. As depicted in FIG. 9, the WiMAX system is generally made up of a core service network (CSN) 1, an access service network (ASN) 2, and a mobile station (MS) 3.
The core service network 1 includes a home agent (HA) 4, a AAA server 5 that performs Authentication/Authorization/Accounting, information collection, etc., and a DHCP server 6. The access service network 2 includes plural access service network gateways 7 and 8, e.g., two in the example depicted and plural base stations (BS) 9, 10, 11, and 12, e.g., two for each of the access service network gateways 7 and 8 in the example depicted.
The access service network gateways 7 and 8 and the base stations 9, 10, 11, and 12 cooperate to perform IP address management for the mobile station 3 and the handover control according to movement of the mobile stations. When two access service network gateways are to be differentiated herein, one is referred to as an access service network gateway A and the other is referred to as an access service network gateway B. For example, the base stations 9 and 10 are connected with the access service network gateway A7; and the base stations 11 and 12 are connected with the access service network gateway B8.
The access service network gateway A7 includes a proxy mobile IP (PMIP) client functioning unit A13, a foreign agent/anchor-data path functioning unit A14, and a DHCP proxy functioning unit A15. Similarly, the access service network gateway B8 includes a proxy mobile IP client functioning unit B16, a foreign agent/anchor-data path functioning unit B17, and a DHCP proxy functioning unit B18. The anchor-data path function is a function of encapsulating user data (packet) by a scheme such as generic routing encapsulation (GRE) to deliver the data to the base stations.
A functional unit with “A” appended to the end of the name of the functional unit (before reference numeral) herein constitutes the access service network gateway A and a functional unit with “B” appended thereto constitutes the access service network gateway B. When the mobile station 3 performs registration with an initial network, an IP address is issued from the home agent 4, the AAA server 5, or the DHCP server 6.
The DHCP proxy functioning unit A15, as a substitute for the DHCP server 6, issues an IP address to the mobile station 3. If DHCP is utilized, an update process is necessary for the issued IP address. If the home address (HoA) of the mobile station 3 is changed, the proxy mobile IP client functioning unit A13 must be notified of a new IP address.
In FIG. 9, when a corresponding node 19 transmits to the internet 20, a packet addressed to the mobile station 3 (assumed to have an IP address: m), the packet arrives at the home agent 4 via the internet 20. The home agent 4 searches a management table and determines a foreign agent functioning unit (assumed to have an IP address: S) of the foreign agent/anchor-data path functioning unit A14 as the transfer destination. The home agent 4 then encapsulates the packet having the destination IP address of m in a packet having the destination IP address of S and transmits the packet using an IP tunneling technology through the R3 data path.
The foreign agent functioning unit of the foreign agent/anchor-data path functioning unit A14 receives the packet addressed thereto and decapsulates the packet to extract the packet having the destination IP address of m. The foreign agent functioning unit searches a management table and determines the base station (assumed to have an IP address: C) as the transfer destination. The foreign agent functioning unit then encapsulates the packet having the destination IP address of m in a packet having the destination IP address of C and transmits the packet using an IP tunneling technology through the R6 data path.
The base station 9 receives the packet addressed thereto and decapsulates the packet to extract the packet having the destination IP address of m. The base station 9 transmits the packet to the mobile station 3. As the mobile station 3 moves, the base station serving as the connection destination of the mobile station 3 is switched as needed. The connection destination after the movement of the mobile station 3 may be the other base station 10 connected to the same access service network gateway A7 as before the movement.
FIG. 10 is a schematic depicting switch-over of the connection destination due to movement of the mobile station. As depicted in FIG. 10, the connection destination of the mobile station 3 after the movement may be the base station 11 connected to the access service network gateway B8 different from that before the movement. In this case, through the handover of the mobile station 3, the foreign agent/anchor-data path functioning unit B17 of the access service network gateway B8 cooperates with the home agent 4 to control the connection, as substitute for the foreign agent/anchor-data path functioning unit A14 of the access service network gateway A7. Such a switch-over may be comprehended as if the foreign agent/anchor-data path functioning unit controlling the connection between a given mobile station and the home agent 4 is moved to another access service network gateway and, therefore, is referred to as relocation.
A mobile terminal control method is known that enables the internet connection to be continued without interruption of data transmission/reception, if the basic service set (BSS) is changed in a mobile terminal connected to the internet through a wireless LAN system due to the handover. This mobile terminal control method includes a detecting step of detecting the change of the BSS due to the handover of the terminal and a control step of making an inquiry with a DHCP server for subnet information while continuing data transmission/reception when the change of the BSS is detected, and further acquiring a new IP address from the DHCP server when a subnet ascertained by the inquiry is different from a subnet before the change of the BSS, and controlling Internet connection using the IP address (see e.g., Japanese Laid-Open Patent Publication No. 2005-124087 (paragraph number)).
A network management system is known that manages terminals to which network IP addresses are automatically distributed. This network management system includes a communication confirming unit that communicates with devices within a network to acquire the network IP addresses of the devices, an IP address inquiring unit that making an inquiry for the distributed network IP addresses with a server that automatically distributes the network IP addresses, a device IP address information storage unit that stores information concerning the network IP addresses of the devices managed in the network, and an automatic device recognizing unit that makes a comparison in response to the notification from the communication confirming unit or the notification from the IP address inquiring unit to output information to indicate that the network IP address is not registered when the network IP address of the notification does not exist (see e.g., Japanese Patent Application Laid-Open Publication No. 2000-270020 (paragraph number)).
However, since the movement of a mobile station is not assumed in the operation of the DHCP proxy functioning unit in the WiMAX system of the conventional proxy mobile IP scheme described above, the following problems occur when the access service network gateway is switched due to the movement of a mobile station. As depicted in FIG. 10, when the access service network gateway is switched from A to B, relocation occurs and the foreign agent/anchor-data path functioning unit B17 of the access service network gateway B8 newly becomes responsible for the connection with the base station 11 and the home agent 4.
However, since the mobile station 3 cannot recognize that the responsibility for the anchor-data path function and the foreign agent function has changed and been given to the foreign agent/anchor-data path functioning unit B17 on the network side, the mobile station 3 makes a request for the update of the IP address to the DHCP proxy functioning unit A15 at the time of the registration to the initial network. Therefore, the foreign agent/anchor-data path functioning unit B17 of the access service network gateway B8 is unable to know the result of the IP address update by the DHCP proxy functioning unit A15 of the access service network gateway A7.
Since the home agent 4 and the foreign agent functioning unit are correlated according to the IP address of the mobile station 3, if the IP address of the mobile station 3 is updated, the relationship between the home agent 4 and the foreign agent functioning unit must be reset. However, if the update result of the IP address of the mobile station 3 is not known, the reset cannot be performed and therefore, the end-to-end communication, i.e., the communication between the mobile station 3 and the corresponding node 19 is no longer sustainable.